I was driving my wife's vehicle the other day and messing with her CD Changer when I was thinking it would be great to have the same type thing in a carpc.
You could have a configuration page that shows 6 or 12 virtual disks. You select (hypothetically) Disk 1 and choose the MP3 CD Directory. You can then select the next disk and do the same.
On the music player screen you change disk on the fly or shuffle between all of them.
Just a thought.